In the electronics industry, it is conventional practice to provide shelves in electronic apparatus, the shelves having receiving stations for sliding reception of circuit packs. A circuit pack conventionally comprises at least one circuit board to be received within a shelf, and a faceplate mounted at a front of the circuit board to be seen from outside the shelf with the circuit pack mounted in position. To hold a circuit pack correctly in an operating position in its shelf with a connector at the rear of the circuit board held positively in engagement with a an corresponding connector in a back plane, latching devices are used. These latching devices are mounted upon the faceplate of the circuit pack and have latched positions in which they engage into recesses in the shelf when the circuit pack is in its operating position. Each latching device needs to be pivoted out of its latched position for removal of its circuit pack, movement out of the latched position also serving to provide leverage to the latching device for urging the circuit pack forwards out of its operating position.
There is a problem which presents itself in cases where electrical cables are required at the fronts of shelves for connection to electrical connectors facing forwardly from the circuit packs. In these cases, difficulty has been found in positional control of the cables which tend to extend haphazardly across the fronts of circuit packs other than the individual packs which the cables actually serve. Hence, in at least some positions along a shelf, in order to remove a circuit pack, the haphazardly placed cables need to be flexed aside from the path of movement of the circuit pack to enable it to be removed from its shelf. Later insertion of a circuit pack then again requires flexing of cables out of the path of the circuit pack. These cable movements serve to unduly stress cable which may eventually result in damage occurring to the cable. The cable movement may be tedious and difficult to perform if cables are to be kept out of contact with a circuit pack during its removal and insertion into a shelf.
In addition, in certain situations, e.g. when circuit packs are held in shelves at central offices, security of electronic equipment may not be a consideration and restrictions need not be placed upon freedom for any person to remove from and insert circuit packs into the shelves. However, should security requirements be necessary, e.g. when installed in customers' premises, it is not unusual to render a latching device immovable when in its latched position so as to prevent circuit pack removal by unauthorized persons. Latching devices are normally rendered immovable by the use of securing members such as quick release pins or screws which are secured to the faceplates.
The above use of securing members also lessens the possibility of removal of a circuit pack from its shelf in error. In cases of such use, it is considered that error in circuit pack removal is less likely to occur if personnel are required to release a securing member before a latching device can possibly be moved out of its latched position. This is because to release the securing member provides more time for the person performing this function to realize that a mistake is being made. Securing members conventionally extend through securing member receiving orifices defined through the latching devices.
In certain other circuit pack constructions it is desirable to remove faceplates from their circuit boards while the circuit boards remain in their operating positions in shelves. This enables test connectors to be reached at the fronts of the shelves for test purposes during operating conditions of the circuit boards. These faceplates are normally secured by securing members to faceplate mounts of the circuit packs so as to allow for complete removal of the circuit packs commenced by movement of the latching devices out of the latched positions, as discussed above. To allow a faceplate to be removed conveniently from its faceplate mount when in the shelf, the securing members may be reached through access orifices provided in the latching devices. Removal of these securing members then permits faceplate withdrawal from its mount during normal pivoting of the latching devices out of their latched positions.
To provide for all the requirements of the above constructions, some latching devices are required without the necessary apertures, i.e. when there are no security requirements relating to circuit pack removal; other latching devices are required with apertures for security reasons or faceplate removal. Normally, latching devices are made from die cast metal parts at inordinate expense particularly when some, but not all, of these devices are required with apertures. Apart from requiring therefore two different structures of latching device, the apertures need to be machine made which is an expensive procedure.